As a polarizing plate protective film, well known have been polymer films, for example, cellulose ester, polyethylene telephthalate (PET), cycloolephine polymer (COP), polycarbonate (PC). A great many methods to adhere one of these films onto a polarizer typified by polyvinyl alcohol (PVA) have been known.
As a polarizing plate protective film, a cellulose ester film has been used more widely than other thermoplastic films, since adhering•drying with a PVA polarizer smoothly proceeds due to its moderate moisture permeability.
However, since cellulose ester itself shows a hydrophobic nature, a hydrophilic treatment such as an alkali saponification, a corona treatment or a plasma treatment is needed before the adhering process of cellulose ester with PVA.
Among these hydrophilic treatments, alkali saponification has been most widely known. However, since a high temperature and high concentration alkali aqueous solution is used in this method, the workability and working environment is poor. Specifically, with respect to diacetyl cellulose which has been traditionally used as an optical film such as a λ/4 film, there has been a problem that a part of the film is dissolved into the alkali solution and the deposited stuff thereof contaminates the process. Accordingly, a surface hydrophilic treatment other than an alkali saponification method has been desired.
As a surface hydrophilic treatment which replaces the alkali saponification, for example, a corona treatment and a plasma treatment have been examined so far (for example, refer to Patent Documents 1 and 2).
However, in order to provide a sufficient hydrophilic property employing these methods, a strong treatment is required. In such a treatment, there have been problems, for example, contamination of the process due to deposition of white foreign substance formed by the decomposition of the film, and increase in film haze, accompanied by lowering of front contrast when used in a liquid crystal display. Specifically, it has been known that the protective film provided on the liquid crystal cell side largely affects the front contrast of a liquid crystal display.